The metasoma is the posterior part of the body, or tagma, of
arthropods whose body is composed of three parts, the other two being
the prosoma and the mesosoma.[1] In insects, it contains most of the
digestive tract, respiratory system, and circulatory system, and the
apical segments are typically modified to form genitalia. In a few of
the most primitive insects (the Archaeognatha), the metasomal segments
bear small, articulated appendages called "styli", which are often
considered to be vestigial. There are also pre-apical appendages in
most insect orders, called cerci, which may be multi-segmented and
almost resembling a posterior pair of antennae; these may be variously
modified, or lost entirely. Otherwise, most adult insects lack
appendages on the metasoma, though many larval insects (e.g.,
caterpillars) have some form of appendages, such as prolegs or, in
aquatic insects, gills.
In apocritan
HymenopteraHymenoptera (wasps, bees and ants), the metasoma consists
of the second abdominal segment (which typically forms a petiole) and
those segments posterior to it, and is often called the gaster rather
than referring to it as the "abdomen"; in these insects, the first
abdominal segment is called the propodeum and is fused to the thorax.
The metasoma is armoured with chitinous plates on the upper surface by
the tergites and on the lower surface by the sternites.[2]
In scorpions, the metasoma is the tail.[3] In other chelicerates, such
as spiders, the mesosoma is fused with the metasoma to form the
opisthosoma.[1]
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